Hi, sorry I've just noticed that you haven't had any answers yet, roundup contains glyphosate which is a CONTACT weedkiller, and is neutralized when it comes onto contact with the soil, so as long as you don't get any on the actual hedge, it wont be harmed, but it's going to be a long slow process at that length of hedge, to paint it on, if they're annual weeds you could just hoe them off, and if you just haave the odd perennial weed, dig them out as you go, Derek.